Known procedures for vision correction like PRK, LASIK, and LASEK are typically used to correct myopic and hyperopic vision errors with or without astigmatism by utilizing a volumetric ablation. In customized treatments also higher order aberrations of the eye can be addressed.
The applicability of known treatment procedures depends on certain parameters, e.g., the corneal thickness of an eye. That is, in case the remaining corneal thickness after applying one of the above vision correction treatments is below a required minimum thickness the eye cannot be corrected in this way. Due to such exclusion criteria, not all potentially correctable eye aberrations can actually be corrected by the application of the above vision correction procedures.
Also, known laser correction treatments may cause an unintended biodynamic effect in the cornea and consequently affect the vision error correction, i.e., the biodynamic effect deteriorates the accuracy of the treatment As an example, to correct a myopic vision error corneal tissue is removed from a central portion of the eye to flatten the cornea. The biodynamic effect of the cornea caused by this treatment may lead to an induced spherical aberration. Therefore, additional corneal tissue has to be ablated to correct the induced error.
According to WO-A-2004/002382, from Technolas GmbH, a method for providing a LASIK or LASEK myopia correction comprises a controlled biodynamic ablation. An ablation ring outside of the optical zone produces a biodynamic flattening of the central region of the cornea which, in turn reduces the ablation depth of corneal tissue in the optical zone to effect a myopia correction.